Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Limiting current, rotating disk electrode voltammetry

The first voltammetric methods met are stationary voltammetries performed on a dropping mercury electrode (polarography) or on a solid rotating disk electrode. The limiting current measured is directly proportional to the concentration of the electroactive species in the solution. Experimental potential scan rate is lower than lOrnVs-1. [Pg.163]

Note HRP Horseradish peroxidase TMB Tetramethylbenzidine ACV Alternating-current voltammetry amole le-18 moles DPV DifTerential pulse voltammetry E Detection limit for unconjugated enzyme E Detection limit for conjugated (Ab/Ag) enzyme FIA-EC Flow-injection analysis with electrochemical detection CC Classy carbon LC-EC Liquid chromatography with electrochemical detection P Detection limit for final enzymatic product P Detection limit for standards of P RDE Rotating disk electrode SPE Screen-printed electrode SQV Square-wave voltammetry zmole le-21 moles. [Pg.5448]

Using cyclic voltammetry of Fe(CN)6 at a rotating disk electrode, Schlenoff provided evidence that decreases in Faradaic current due to the presence of P S S/poly(diallydimethylammonium chloride) occur because of slow movement of Fe(CN)6 through the film [37]. Peak currents are independent of potential suggesting that diffusion rather than kinetics is limiting current. This is in agreement... [Pg.6421]

While the voltammograms can be quantitatively analyzed to yield permeant transport parameters - for example, via numerical simulations - we have instead utilized rotating disk electrode (RDE) voltammetry for this purpose. Sequential solution and film transport problems are generally well described by a variant of the Koutecky-Levich analysis [11]. This analysis represents the series process Idnetically as a reciprocal sum of pure solution-phase convection/dilFusion (cd) and pure film permeation (p) rates or fluxes. Since detection is electrochemical, the fluxes can be written in terms of currents, where ilim is the observed overall, mass-transport limited, current [12] ... [Pg.6433]

The rotating disk electrode is becoming one of the most powerful methods for studying both diffusion in electrolytic solutions and the kinetics of moderately fast electrode reaction because the hydrodynamics and the mass-transfer characteristics are well understood and the current density on the disk electrode is supposed to be uniform. Levich [179] solved the family of equations and provided an empirical relationship between diffusion limiting current (id) and rotation rate ( >) as shown in Eq. (9.42). In particular applications in fuel cells, the empirical relationship which is given by Levich was also used in linear scan voltammetry (LSV) experiment performed on a RDE to study the intrinsic kinetics of the catalyst [151,159,180-190]. However, it is more appropriate to continue the discussion later in detail in the LSV section. [Pg.239]

Linear sweep voltammetry (LSV) in combination with a rotating disk electrode (RDE) is a widely used technique to study electrode kinetics. Different methods exist to extract the values of the process parameters from polarization curves. The Koutecky-Levich graphical method is frequently used to determine the mass transfer parameters (Diard et al., 1996) the slope of a plot of the inverse of the limiting current versus the inverse of the square root of the rotation speed of the rotating disk electrode is proportional to the diffusion coefficient. If more than one diffusing species is present, this method provides the mean diffusion coefficient of all species. The charge transfer current density is determined from the inverse of the intercept. In practical situations, however, the experimental observation of a limiting current... [Pg.21]

As mentioned in the introduction of the amperometry techniques, the voltammetry with periodical renewal of the diffusion layer is particularly effective in monitoring a process differently involving an electroactive species, e.g., in the already mentioned amperometric titrations, in the determination of the stability of a species, etc. In particular cases, also simple chronoamperometry, i.e., at a fixed, suitably chosen potential, may be effective to this purpose. Noteworthy, it will be clear in the following that the much more widely diffused linear potential scan and cyclic voltammetric techniques are not always suitable to substitute for voltammetry with periodical renewal of the diffusion layer to the purpose of monitoring electroactive species during their transformation. Voltammetry with periodical renewal of the diffusion layer, as well as the voltammetry at rotating disk electrode, only allows the estimation of the concentrations of both partners of a redox couple, on the basis of the ratio between the anodic and cathodic limiting currents. [Pg.264]

As the field of electrochemical kinetics may be relatively unfamiliar to some readers, it is important to realize that the rate of an electrochemical process is the current. In transient techniques such as cyclic and pulse voltammetry, the current typically consists of a nonfaradaic component derived from capacitive charging of the ionic medium near the electrode and a faradaic component that corresponds to electron transfer between the electrode and the reactant. In a steady-state technique such as rotating-disk voltammetry the current is purely faradaic. The faradaic current is often limited by the rate of diffusion of the reactant to the electrode, but it is also possible that electron transfer between the electrode and the molecules at the surface is the slow step. In this latter case one can define the rate constant as ... [Pg.381]

This equation corresponds to the Lineweaver-Burk kinetic equation (Lyons et al., 1992, 1994) and can be transformed into an equation giving the dependence of kinetic currents, 4, on the concentration of substrate in the solution bulk. Values of /), at different concentrations of substrate can be determined from the limiting, steady-state currents, tht.i, obtained, for instance, as plateau currents in rotating disk voltammetry, using Equation (3.6). For the case of thin films with a surface concentration of catalytic centers (rnol/crn ) over an electrode of area A, one can write ... [Pg.60]

A solution of volume 50 cm contains 2.0 X 10 M Fe and 1.0 X 10 M in 1 M HCl. This solution is examined by voltammetry at a rotating platinum disk electrode of area 0.30 cm. At the rotation rate employed, both Fe and have mass-transfer coefficients, m, of 10 cm/s. (a) Calculate the limiting current for the reduction of Fe under these conditions, (b) A current-potential scan is taken from +1.3 to —0.40 V vs. NHE. Make a labeled, quantitatively correct, sketch of the i-E curve that would be obtained. Assume that no changes in the bulk concentrations of Fe and Sn " occur during this scan and that all electrode reactions are nemstian. [Pg.42]


See other pages where Limiting current, rotating disk electrode voltammetry is mentioned: [Pg.472]    [Pg.500]    [Pg.531]    [Pg.382]    [Pg.362]    [Pg.114]    [Pg.115]    [Pg.490]    [Pg.230]    [Pg.54]    [Pg.148]    [Pg.555]    [Pg.589]    [Pg.605]    [Pg.137]    [Pg.360]    [Pg.131]    [Pg.285]    [Pg.208]    [Pg.646]    [Pg.230]    [Pg.555]    [Pg.589]    [Pg.605]    [Pg.256]    [Pg.144]    [Pg.649]    [Pg.278]    [Pg.145]    [Pg.87]    [Pg.256]    [Pg.314]    [Pg.927]    [Pg.651]    [Pg.331]    [Pg.202]    [Pg.393]    [Pg.158]    [Pg.267]   
See also in sourсe #XX -- [ Pg.150 ]




SEARCH



Current limit

Disk current

Electrodes rotator

Limitation current

Limited currents

Limiting current electrodes

Limiting currents

Rotating disk electrode

Rotating disk electrode voltammetry

Voltammetry current

© 2024 chempedia.info